Hearing aids for providing a user selectable directional response have become quite popular in the marketplace. In a noisy environment, the user of such an aid can select the directional pattern and thus eliminate some of the noise coming from the rear. This can increase the signal to noise level enough to improve the intelligibility of speech originating from the forward direction. In a quiet environment, the user would normally switch to the nondirectional pattern in favor of its better performance in quiet.
One way to achieve a directional response in a hearing aid is to use two omnidirectional microphones, and to combine their electrical signals to form the directional beam. Compared to the use of a directional microphone, the Dual Omni approach has some advantages. However, it also carries the requirement that the response of the two microphones be accurately matched in magnitude and phase. The matching must be accurate throughout the frequency band where directionality is needed, and must remain matched throughout the life of the hearing aid. Normal variations in microphone manufacturing do not provide a close enough match for most applications.
Often it has been necessary to specially measure and select the microphones for use in a paired application. The present invention presents an apparatus and method of compensation for the variations in microphone performance. An electrical circuit is used with one or both of the microphones to achieve the necessary match in response for directional processing. The response of the circuit can be “tuned” to each microphone at the final stages of manufacturing, as a part of the fitting porches, automatically, or even at a periodic follow-up visit if the characteristics of the microphone have changed through aging or abuse.